This application claims the benefit of Japanese patent application No. Heisei 09-277021, filed Oct. 9, 1997 and Japanese Patent Application No. Heisei 10-059579, filed Mar. 11, 1998, which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a manufacturing method of synthetic silica glass.
2. Discussion of the Related Art
Currently, stepper are being used for photolithography to expose and transcribe very small integrated circuit patterns on, for example, semiconductor substrates during the manufacturing process of semiconductor devices. Recently, due to a higher integration of Large Scale Integrated Circuits (LSI), ultraviolet light, which has shorter wavelengths than visible light, has been used in the stepper""s light source. Therefore, an optical system of an exposure apparatus must include components that transmit light in the ultraviolet range, since conventional optical glass is impractical to use in such applications. One known example of an optical material with a high transmittance in the ultraviolet range is silica glass.
In addition, the optical system of the exposure apparatus includes multiple optical members, such as lenses, which are used for adjusting for aberrations. Therefore, in order to have a high transmittance for the entire optical system of the exposure apparatus, each individual optical member must have a high transmittance. In order to increase the transmittance of silica glass, the silica glass must have a high purity. One known manufacturing method by which high purity silica glass can be obtained is a flame hydrolysis method (sometimes called a xe2x80x9cdirect methodxe2x80x9d or a xe2x80x9cdirect flame hydrolysis methodxe2x80x9d).
For the flame hydrolysis method, a silicon compound with high purity, such as silicon tetrachloride (SiCl4) is used. This compound, along with a combustion gas and a combustible gas (such as oxygen and hydrogen), which are used for heating and for the hydrolysis reaction, are expelled from a burner toward a target in a synthesis furnace. The target is rotated and lowered in the synthesis furnace. The starting material expelled from the burner is hydrolyzed by the oxygen/hydrogen flame and forms minute silica glass particles (soot). The soot is deposited, fused, becomes transparent, and forms an ingot of silica glass. The silica glass thus obtained is called synthetic silica glass.
The higher the chlorine concentration in the synthetic silica glass, the lower the durability to ultraviolet radiation of the synthetic silica glass. Therefore, in order to lower the chlorine concentration in the synthetic silica glass, it is preferable to use chloride-free silicon compounds.
When silicon chloride compounds are used, hydrogen chloride, which is a corrosive gas, is generated in the synthesis furnace. To avoid generating hydrogen chloride, it is preferable to use silicon compounds, which are not chlorides, as a starting material for synthetic silica glass.
An example of a technology for using chloride-free organic silicon compounds as a starting material for synthetic silica glass is disclosed in xe2x80x9cTokukaiheixe2x80x9d (publication of unexamined patent application) Heisei 4-270130 (1992) (corresponding to U.S. Pat. No. 5,043,002).
Compared to the boiling point of SiCl4, which is 58xc2x0 C. to 59xc2x0 C., the boiling point of many organic silicon compounds is 100xc2x0 C. or more, due to their high molecular weight. However, heat resistance of even the heat-resistant versions of commercial mass flow meters used for gases, is, at most, only 80xc2x0 C. Therefore, it has been difficult to control the amount of the gaseous organic silicon compound introduced into the synthesis furnace.
Therefore, there is a need for a manufacturing method for synthetic silica glass that can control the amount of a silicon compound having a high boiling point when introduced to the synthesis furnace.
Accordingly, the present invention is directed to a method of manufacturing of synthetic silica glass that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a better controlled method of manufacturing of synthetic silica glass.
Another object of the present invention is to provide a manufacturing method of synthetic silica glass where a material solution is supplied in a stable manner to the vaporizer.
Another object of the present invention is to improve the precision of flow control of the material solution using a liquid mass flow meter.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, in one aspect of the present invention there is provided a manufacturing method of synthetic silica glass including the steps of introducing a liquid silicon compound into a vaporization equipment, wherein an amount of the liquid is controlled with a liquid mass flow meter 20, converting the liquid into a gaseous silicon compound, and supplying the gaseous silicon compound into a synthesis furnace to form synthetic silica glass.
In another aspect of the present invention there is provided a method of manufacturing synthetic silica glass including the steps of pressurizing a liquid storage tank including a liquid silicon compound therein, displacing the liquid silicon compound into a vaporization equipment while controlling an amount of the liquid silicon compound displaced by a liquid mass flow meter 20, mixing the liquid silicon compound with a carrier gas to generate a gaseous silicon compound, injecting the gaseous silicon compound into a synthesis furnace, and forming synthetic silica glass by hydrolyzing the gaseous silicon compound in the synthesis furnace.
In another aspect of the present invention there is provided a manufacturing method for synthetic silica glass including the steps of generating bubbles in a liquid silicon compound using a foamer, removing the bubbles using a degassed, introducing the liquid silicon compound into a vaporizer, vaporizing the liquid silicon compound to produce a vapor; and introducing the vapor into a synthesis furnace to form synthetic silica glass, wherein a flow rate of the liquid silicon compound is controlled using a liquid mass flow meter.
In another aspect of the present invention there is provided a method of manufacturing synthetic silica glass including the steps of generating bubbles in a liquid silicon compound using a foamer, removing the bubbles using a degassed, introducing the liquid silicon compound into a vaporizer, wherein an amount of the liquid silicon compound is controlled with a liquid mass flow meter, converting the liquid silicon compound into a gaseous silicon compound, and supplying the gaseous silicon compound into a synthesis furnace to form synthetic silica glass.
In another aspect of the present invention there is provided a method of manufacturing synthetic silica glass including the steps of pressurizing a liquid storage tank including a liquid silicon compound therein, generating bubbles in the liquid silicon compound using a foamer, removing the bubbles using a degasser, displacing the liquid silicon compound into a vaporizer while controlling an amount of the liquid silicon compound displaced by a liquid mass flow meter, mixing the displaced liquid silicon compound with a carrier gas to generate a gaseous silicon compound, injecting the gaseous silicon compound into a synthesis furnace, and forming synthetic silica glass by hydrolyzing the gaseous silicon compound in the synthesis furnace.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.